How to Lodge BAS as a Sole Trader in Australia (2025-26 Guide)

If you're registered for GST and running a business as a sole trader, you need to lodge a Business Activity Statement (BAS). For a lot of people, BAS time brings a mix of dread and confusion — what numbers go where, what happens if you're late, and whether you've been putting enough aside throughout the quarter.

This guide walks through every part of the process: what a BAS actually contains, when it's due, how to calculate your GST figures correctly, and how to lodge. It's written for Australian sole traders in 2025-26 using current ATO figures.

Quick answer: As a sole trader, you lodge a BAS quarterly (or monthly if turnover exceeds $20M). The quarterly due dates for 2025-26 are 28 Oct, 28 Feb, 28 Apr, and 28 Jul. You report GST collected from customers, GST paid on business purchases, and any PAYG instalments. Lodge via myGov, the ATO Business Portal, or accounting software registered with the ATO.

This is general information, not tax advice — see your registered tax agent for your specific situation.

What Is a BAS?

A Business Activity Statement is a form you submit to the ATO to report and pay taxes related to your business activity. For most sole traders, it covers:

  • GST collected — the 10% GST you charged customers and received
  • GST paid (input tax credits) — the 10% GST you paid on eligible business purchases
  • PAYG instalments — pre-payments toward your end-of-year income tax (if the ATO has enrolled you)
  • PAYG withholding — if you employ staff and withhold tax from their wages

You don't need a BAS if you're not registered for GST. Registration becomes mandatory once your GST turnover hits $75,000 in any 12-month period (actual or projected). See ato.gov.au for full details.

How Often Do You Lodge?

Quarterly (most sole traders)

If your GST turnover is under $20 million, you lodge quarterly. This is the default for almost every sole trader.

Monthly

If your GST turnover is $20 million or more, you must lodge monthly.

Annual

Some small businesses with turnover under $75,000 who have voluntarily registered for GST can opt for annual lodgment. However, you still need to pay a GST instalment quarterly — you reconcile at year end.

2025-26 BAS Due Dates (Quarterly)

Quarter Period Covered Due Date
Q1 1 July – 30 September 2025 28 October 2025
Q2 1 October – 31 December 2025 28 February 2026
Q3 1 January – 31 March 2026 28 April 2026
Q4 1 April – 30 June 2026 28 July 2026

Important: If you lodge through a registered BAS agent or tax agent, you may get extended due dates. Confirm with your agent or check ato.gov.au for the current lodgment program.

If the due date falls on a weekend or public holiday, you generally have until the next business day. Verify with the ATO for any specific year variations.

How to Calculate Your GST Figures

This is the part that trips people up most. Here's the maths.

GST Collected (what you owe the ATO)

If you charge GST-inclusive prices, the GST component is calculated using the 1/11th method.

Formula: GST collected = Total GST-inclusive revenue / 11

Example: You ran a cafe and took $33,000 in GST-inclusive revenue for the quarter.

GST collected = $33,000 / 11 = $3,000

That $3,000 belongs to the ATO — it's not your money, you've just been holding it.

GST Paid / Input Tax Credits (what the ATO owes you)

You can claim back the GST you paid on business expenses — supplies, ingredients, equipment, software, fuel and so on — as long as they're for a creditable purpose.

Formula: GST paid = Total GST-inclusive business expenses / 11

Example: You spent $11,000 (GST-inclusive) on coffee beans, packaging and equipment during the quarter.

GST paid = $11,000 / 11 = $1,000

Net GST Position

Net GST payable = GST collected − GST paid = $3,000 − $1,000 = $2,000 to pay

If your input tax credits exceed GST collected (common when you've bought expensive equipment), you'll get a refund.

What Counts as a Creditable Purchase?

Not every expense is claimable. The purchase must be:

  • For a business purpose (not private use)
  • From a GST-registered supplier
  • Supported by a valid tax invoice

Personal expenses, residential rent, and wages are not subject to GST and cannot generate input tax credits.

PAYG Instalments on Your BAS

If the ATO has enrolled you in PAYG instalments, you'll see a separate section on your BAS (usually T1–T9 fields). This is separate from GST.

PAYG instalments are pre-payments of your expected income tax for the year. The ATO generally enrols you when your tax bill from business or investment income exceeded $4,000 in your most recent tax return.

You have two options:

Option 1 — Instalment amount (T7): The ATO calculates a fixed dollar amount each quarter based on your previous return. You pay it unless you vary.

Option 2 — Instalment rate (T1 and T2): The ATO gives you a rate. You apply that rate to your actual income each quarter. More work, but more accurate if your income fluctuates.

You can vary your instalment if you expect your income to be lower than the ATO assumes. Just be careful: if you vary down and end up underpaying by more than 15% of what you should have paid, you may be charged a penalty. See ato.gov.au for current variation rules.

Fuel Tax Credits

If you use fuel in your business for eligible activities — heavy vehicles, machinery, plant equipment, marine vessels, light vehicles off public roads — you may be able to claim fuel tax credits on your BAS.

This is most relevant for primary producers, miners, and businesses running large machinery. Most urban sole traders won't qualify. Check the ATO fuel tax credits page for rates and eligibility.

How to Lodge Your BAS

Option 1: myGov (most sole traders)

  1. Log in to myGov and link the ATO service
  2. Go to Business → Activity Statements
  3. Select the open lodgment period
  4. Enter your GST and PAYG figures
  5. Review and submit
  6. Pay any amount owing via BPAY, credit card or direct debit

Option 2: ATO Online Services for Business (Business Portal)

If you have a myGovID (the app) and an ABN linked, you can access the ATO Business Portal directly. Same process as myGov but accessed via a separate login.

Option 3: Registered Tax or BAS Agent

A BAS agent lodges on your behalf and often gets extended due dates. If you're spending more time on BAS than you'd like, this is worth considering.

Option 4: Accounting or Bookkeeping Software

Xero, MYOB, and other ATO-integrated software can pre-fill and lodge your BAS directly. Some software connects to the ATO and pulls your transaction data automatically. Summed (mentioned below) handles the BAS prep side — calculating GST collected and paid from your transactions — so your numbers are ready when lodgment time comes.

What Happens If You Lodge Late?

Missing a BAS due date has two consequences:

1. Failure to Lodge (FTL) penalty The ATO charges penalty units for late lodgment. For medium-to-large businesses, this scales. For small businesses (turnover under $1M), the penalty is lower per period but still applies. Check ato.gov.au for current penalty unit values.

2. General Interest Charge (GIC) If you lodge late AND have an amount owing, the ATO charges GIC on the unpaid debt. The GIC rate changes quarterly. See the ATO website for the current rate.

The ATO can and does waive first-time penalties if you have a clean history and request remission. But it's far easier to just lodge on time — even if you can't pay immediately. Lodging and paying are separate acts. If you can't pay, lodge anyway and contact the ATO to arrange a payment plan.

Keeping Records

You need to keep all records supporting your BAS for five years. This includes:

  • Tax invoices for all purchases you claim input tax credits on
  • Records of all sales (invoices, POS reports, bank deposits)
  • Receipts for expenses
  • Logbooks if claiming vehicle expenses

The ATO can audit any BAS period within this window.

Tools That Make This Easier

Tracking GST manually in a spreadsheet works when you're just starting out, but it gets messy fast. By the time you're doing $30,000+ a quarter, you want a system that separates GST-inclusive amounts automatically, tracks which expenses are claimable, and totals everything by quarter so you're not scrambling on lodgment day.

Summed handles BAS prep automatically — try it free for 30 days at $9/mo. Start free →

FAQ

Q: Do I need to lodge a BAS if I have no income for the quarter?

A: If you're registered for GST, yes — you still need to lodge a nil BAS. It's a five-minute job: enter zeros and submit. Failing to lodge, even a nil, still attracts a potential penalty.

Q: Can I lodge BAS early?

A: Yes. You can lodge as soon as the quarter ends. If you're well-organised, lodging early means you know your tax position earlier and can plan your cash flow accordingly.

Q: What if I realise I made an error on a lodged BAS?

A: You can correct minor errors on your next BAS (there are limits on what qualifies as a "minor" error — generally under $10,000 net GST effect). For larger errors, you need to revise the original BAS. Do this through the same lodgment channel you used originally, or contact the ATO.

Q: I'm GST-registered but I had a loss this quarter. Do I still pay GST?

A: If your GST collected is more than your input tax credits, yes. A business loss is a separate calculation — it's about income tax, not GST. You could have a loss for income tax purposes but still owe GST.

Q: What's the difference between BAS and tax return?

A: BAS is lodged quarterly and covers GST and PAYG instalments. Your annual tax return is lodged once a year and covers your total income, deductions, and final income tax position. PAYG instalments paid on your BAS are a credit against the tax calculated in your annual return.

Q: Do I pay GST on overseas sales?

A: Generally no — most exports of goods and services to overseas customers are GST-free (0% rate). However the rules can be complex for digital services and some other scenarios. Check ATO guidance for your specific situation.

Q: What's the penalty for not lodging BAS at all?

A: The ATO can raise a default assessment (essentially guessing your liability) and apply Failure to Lodge penalties. Continued non-compliance can lead to director penalty notices if you're a company director, and ultimately prosecution. Don't ignore it — even if you can't pay, lodge and call the ATO.

Q: My income is seasonal. Can I vary my PAYG instalments?

A: Yes. You can vary your PAYG instalment amount on each quarterly BAS. Just be mindful of the 15% under-variation threshold — if you vary too far down from what you should pay, you may face a penalty. If your income is genuinely lower, a well-supported variation is fine.